Circle Packing is a variation of a Treemap that uses circles instead of rectangles. Containment within each circle represents a level in the hierarchy: each branch of the tree is represented as a circle and its sub-branches are represented as circles inside of it. The area of each circle can also be used to represent an additional arbitrary value, such as quantity or file size. Colour may also be used to assign categories or to represent another variable via different shades.
As beautiful as Circle Packing appears, it’s not as space-efficient as a Treemap, as there’s a lot of empty space within the circles. Despite this, Circle Packing actually reveals hierarchal structure better than a Treemap.